Analysis and quantification of lipid peroxidation products in the postprandial period of subjects fed a controlled diet

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Postprandial lipemia has been suggested to be a risk factor for cardiovascular disease. Levels of oxidized postprandial low-density lipoprotein have been shown to result in a higher degree of cholesterol accumulation while soy protein isoflavones have been found to inhibit lipid peroxidation in vitro. The goal of this study was to quantify serum concentrations of lipid peroxidation products in the postprandial period of human subjects fed a controlled diet containing soy protein with or without isoflavone supplement. Postprandial serum samples were collected from 23 men aged 18-30, divided into three groups studied (milk protein vs. soy protein with additional isoflavones vs. soy protein without additional isoflavones). Four main oxidatively modified derivatives of linoleic acid; 9 S -hydroxy-10 Z, 12 E -octadecadienoic acid (9-HODE), 9 S -hydroperoxy-10 Z, 12 E -octadecadienoic acid (9-HpODE), 13 S -hydroxy-9 Z, 11 E -octadecadienoic acid (13-HODE) and 13 S -hydroperoxy-9 Z, 11 E -octadecadienoic acid (13-HpODE) were analyzed by RP-HPLC. The concentrations of each analyte during the postprandial period were analyzed by area-under-curve analysis, before the diet and after the participants had been on the diets for four weeks. Analysis of variance testing indicated that the most substantial decrease in the concentrations of the four lipid peroxidation products analyzed occurred within the milk protein group and the soy protein without additional isoflavones group. These results indicate that soy protein enriched with isoflavones does not inhibit the oxidation of linoleic acid in vivo.